Recording material detection apparatus and image forming apparatus

ABSTRACT

A recording material detection apparatus having a detecting device configured to detect a surface state of a recording material on the basis of reflected light from a surface of the recording material includes a reference surface to be irradiated with light from a light source, the detecting device includes a light-shielding portion configured to control conditions for detecting information relating to the surface state of the recording material on the basis of the reflected surface from the reference surface, and cover a portion of the reference panel other than the reference surface so as to prevent the light from the light source from being reflected from the portion of the reference panel other than the reference surface and being received by the light-receiving unit.

CROSS REFERENCE OF RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.13/307,537 filed on Nov. 30, 2011 which claims the benefit of JapanesePatent Application No. 2010-276166 filed Dec. 10, 2010, which is herebyincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording material detectionapparatus configured to detect a surface state of a recording materialby irradiating the recording material with light and an image formingapparatus having such a recording material detection apparatus.

2. Description of the Related Art

Image forming apparatuses such as copying machines or laser beamprinters are configured to transfer an developer image(toner image)visualized by a developing device on a recording material underpredetermined conditions (for example, transfer biases and recordingmaterial conveyance speeds at the time of transfer). Then, by heatingand pressurizing the recording medium having the developer imagetransferred thereon under predetermined fixing conditions (for example,fixing temperatures and recording material conveyance speeds at the timeof fixing), the developer image is fixed to the recording material.

There is an image forming apparatus including a recording materialdetecting unit configured to irradiate a recording material with lightfrom a light source and detect a surface state of the recording medium,and configured to determine the types of recording materials on thebasis of the result of detection of the recording material detectingunit and control the transferring conditions and fixing conditions.

Such a recording material detecting unit is capable of detecting therecording material stably by controlling the conditions of detection ofthe recording materials via an adjustment for achieving irradiation witha stable amount of the light from the light source and a shadingcorrection for correcting unevenness of amount of light on the surfaceof the recording material. More specifically, the amount-of-lightadjustment of the light source and the shading correction are enabled byirradiating a reference panel (white reference) with the light from thelight source and detecting reflected light therefrom.

Now, Japanese Patent Laid-Open No. 1-099187 discloses a configuration ofa reference panel in which the reference panel is movably arranged onthe side of a light-receiving unit with respect to the surface of therecording material (in a unit) and is moved to a reading position whenneeded in order to avoid the dirt or scratches on the reference paneldue to the recording materials being conveyed or dust existing in theperiphery thereof.

However, with the reference panel having a movable configuration, themechanism becomes complicated correspondingly, and an increase in thesize of the apparatus and a cost increase are resulted.

SUMMARY OF THE INVENTION

The present invention provides a reduction of a noise caused byreflected light from a portion other than a reference surface of areference panel and inhibition of a reduction of a range from which animage of a surface of a recording material to be used for determinationof the recording material is acquired.

The present invention also provides an image forming apparatusconfigured to form an image on a recording material including: a lightsource configured to irradiate a recording material with light; areference panel having a reference surface to be irradiated with lightfrom the light source, and a light-receiving unit having a plurality ofpixels and configured to receive light reflected from a surface of therecording material irradiated with the light from the light source andthe reference surface, the reference panel being arranged on the side ofthe light-receiving unit with respect to part of the surface of therecording material which reflects the light toward the light-receivingunit in the direction orthogonal to the surface of the recordingmaterial, and being configured to detect information on a surface stateof the recording material on the basis of the reflected light from thesurface of the recording material received by the light-receiving unit,control conditions of formation of the image on the recording material,and control conditions of detection of the information on the surfacestate of the recording material on the basis of the reflected light fromthe reference surface received by the light-receiving unit, and alight-shielding portion configured to cover a portion of the referencepanel other than the reference surface so as to prevent the light fromthe light source from being reflected from the portion of the referencepanel other than the reference surface and being received by thelight-receiving unit.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a recording material detecting unitviewed from a downstream side of the direction of conveyance of arecording material.

FIG. 1B is an enlarged view of a portion indicated by IB in FIG. 1A.

FIG. 2 is a perspective view of an interior of a recording materialdetecting unit.

FIG. 3 is an operation control block diagram of the recording materialdetecting unit.

FIG. 4 is a chart showing a distribution of brightness (amount of light)of light received by a receiving unit.

FIG. 5 is a cross-sectional view of the recording material detectingunit viewed from a direction parallel to the surface of a recordingmaterial and orthogonal to the direction of conveyance of the recordingmaterial.

FIG. 6 is a schematic cross-sectional view of an image forming apparatushaving the recording material detecting unit mounted thereon.

FIG. 7A is a perspective view showing an interior of the recordingmaterial detecting unit.

FIG. 7B is a cross-sectional view of the recording material detectingunit viewed from a direction parallel to the surface of a recordingmaterial and orthogonal to the direction of conveyance of the recordingmaterial.

FIG. 8 is a drawing showing the recording material detecting unit viewedfrom a direction orthogonal to the surface of the recording material.

FIG. 9 is a cross-sectional view of the recording material detectingunit viewed from a downstream side in the direction of conveyance of therecording material.

FIG. 10 is a chart showing a distribution of brightness (amount oflight) of light received by a receiving unit.

DESCRIPTION OF THE EMBODIMENTS First Embodiment Image Forming Apparatus

Conventional systems disclose a reference panel in which the referencepanel is movably arranged on the side of a light-receiving unit withrespect to the surface of the recording material (in a unit) and ismoved to a reading position when needed in order to avoid the dirt orscratches on the reference panel due to the recording materials beingconveyed or dust existing in the periphery thereof.

However, with the reference panel having a movable configuration, themechanism becomes complicated correspondingly, and an increase in thesize of the apparatus and a cost increase are resulted. Therefore, thereis a configuration having the reference panel fixed on the side of thelight-receiving unit with respect to the surface of the recordingmaterial (within the unit). As an example, a recording materialdetecting unit in which the reference panel is fixed on the side of thelight-receiving unit with respect to the surface of the recordingmaterial (within the unit) as shown in FIGS. 7A, 7B, FIG. 9, and FIG. 8is conceivable.

FIG. 7A is a perspective view showing an interior of a recordingmaterial detecting unit 40. FIG. 7B is a cross-sectional view of therecording material detecting unit 40 viewed from a direction parallel tothe surface of a recording material and orthogonal to the direction ofconveyance of the recording material. FIG. 9 is a cross-sectional viewof the recording material detecting unit 40 viewed from the downstreamside in the direction of conveyance of the recording material.

The recording material detecting unit 40 includes light sources 41 a and41 b configured to irradiate a surface of a recording material P withlight, an imaging lens 42 configured to form an image by the lightreflected from the surface of the recording material P, and a linesensor (light-receiving unit) 43 configured to receive the light of theimage formed by the imaging lens 42 and pick up the image. The lightemitted from the light sources 41 a and 41 b are regulated by slits 44.Reference panels 46 a and 46 b are provided on the side of thelight-receiving unit with respect to the surface of the recordingmaterial P at ends of an area which is irradiated with the light fromthe light sources 41 a and 41 b. Irradiated surfaces of the referencepanels 46 a and 46 b reflect the light from the light sources 41 a and41 b toward the imaging lens 42, and the reflected light is received bythe line sensor 43, whereby the amount-of-light adjustment and theshading correction are performed and the detecting conditions of therecording material detecting unit are controlled. Provided between theimaging lens 42 and the recording material P is a protecting member 47configured to protect the imaging lens 42 from becoming dirty anddamaged and allow passage of the reflected light from the recordingmaterial P therethrough. These members are supported within a unit body.In particular, the reference panels 46 a and 46 b are attached on a backsurface of a portion guiding the conveyance of the recording material Pwith a double-faced adhesive material or the like. Here, the lightsources 41 a and 41 b are arranged so that not only the surface of therecording material P, but also the reference panels 46 a and 46 b areirradiated simultaneously with the light from the light sources 41 a and41 b. Therefore, the reflected light reflected from the surface of therecording material P and the reflected light reflected from thereference panels 46 a and 46 b may be received simultaneously by theline sensor 43.

FIG. 8 is a drawing showing the recording material detecting unit 40viewed from a direction orthogonal to the surface of the recordingmaterial. The longitudinal directions of the imaging lens 42 and theline sensor 43 are arranged so as to be orthogonal to the direction ofconveyance of the recording material P. Optical axes of the lightsources 41 a and 41 b are arranged so as to be inclined with respect tothe direction of conveyance of the recording material P and to intersecteach other. The reference panels 46 a and 46 b are provided so as tocorrespond to the light sources 41 a and 41 b respectively, and arearranged on the outer sides of the optical axes of the light sources 41a and 41 b (on the side of the ends of the line sensor 43).

FIG. 10 shows an example of an amount-of-light distribution of lightreceived by the line sensor 43. A lateral axis represents positions onthe line sensor 43 corresponding to respective pixels, and a verticalaxis represents brightness corresponding to a received amount of light.The pixel position 1 corresponds to a pixel at a left end of the linesensor 43 in FIG. 8, and the corresponding pixel on the line sensor 43in FIG. 8 goes rightward with an increase in the numerical value of thepixel position. Ranges of irradiation on recording material a and bindicate ranges of a surface image of the recording material to beacquired for being used for determination of the type of the recordingmaterial P on the basis of the brightness distribution of the lightirradiated from light sources 41 a and 41 b. Ranges having a brightnessexceeding a predetermined threshold value in this amount-of-lightdistribution are defined as ranges of effective image of the recordingmaterial, and the surface images within these ranges of effective imageof the recording material are used for the determination of the type ofthe recording material P. Here, coupling with a minimum durationrequired for the line sensor 43 to receive the light and the rate ofirregular reflection, the threshold value of the brightness is set to180 in a case where the strength of brightness have 256 tones (0(dark)to 255(bright)). Also, ranges of irradiation on the reference panels aand b on the reference panels 46 a and 46 b represent areas from whichthe surface information of reference surfaces R of the respectivereference panels 46 a and 46 b is acquired. The ranges of effectiveimage of the reference panels a and b are areas used for calculating theamount of reflected light from the reference surfaces R. Here, thereference surfaces R of the reference panels 46 a and 46 b are planeswhich reflect reference reflected light for performing theamount-of-light adjustment and the shading correction to control thedetecting conditions of the recording material detecting unit.

In FIG. 9, an irradiated light irradiated from the light source 41 a tothe surface of the recording material P is shown in a double-dashedchain line represented by L1, an irradiated light irradiated on an endsurface of the reference panel 46 a is shown in a double-dashed chainline represented by L2, and an irradiated light irradiated on thereference surface R of the reference panel 46 a is shown in adouble-dashed chain line represented by L3. As the same goes for theside of the light source 41 b, the side of the light source 41 a will bedescribed as an representative.

In this manner, the light reflected from an end surface E or an edgeportion C between the reference surface R and the end surface E, whichare portions of the reference panel 46 a other than the referencesurface R, enter the range of irradiation on the recording material ofthe line sensor 43 as a noise component (peaks near the pixel positions50 and 420 in FIG. 10). Therefore, the range of effective image of thereference panel should be set to a range which can receive sufficientamount of light while avoiding the noise caused by the reflection fromthe end surface E or the edge portion C, which are the portions of thereference panel 46 a other than the reference surface R, so that areduction of the range of effective image of the recording material isobliged.

First of all, an image forming apparatus having a recording materialdetecting unit according to a first embodiment mounted thereon will bedescribed. FIG. 6 is a schematic cross-sectional view of an imageforming apparatus 1 having a recording material detecting unit 40mounted thereon. Respective configurations of the image formingapparatus 1 will be given below. Reference numeral 2 designates a paperfeed cassette in which a recording material P is stored. Referencenumeral 3 designates a paper feed tray on which the recording material Pis stored in stack. Reference numeral 4 a designates a paper feed rollerconfigured to feed the recording material P from the paper feed cassette2. Reference numeral 4 b designates a paper feed roller configured tofeed the recording material P from the paper feed tray 3. Referencenumeral 5 designates a conveying roller configured to convey thesupplied recording material P, and reference numeral 6 designates anopposed conveying roller opposing the conveying roller 5. Referencenumerals 11Y, 11M, 11C and 11K designate photoconductive drums, whichrespectively carry developers of yellow, magenta, cyan, and black.Reference numerals 12Y, 12M, 12C and 12K designate charging rollers asprimary charging units configured to charge the photoconductive drums11Y, 11M, 11C and 11K uniformly at a predetermined potential. Referencenumerals 13Y, 13M, 13C and 13K are optical units configured toirradiates the photoconductive drums 11Y, 11M, 11C and 11K charged bythe primary charging units with laser beams corresponding to image dataof respective colors, and form electrostatic latent images.

Reference numerals 14Y, 14M, 14C, and 14K designate developing unitsconfigured to visualize the electrostatic latent images formed on thephotoconductive drums 11Y, 11M, 11C and 11K. Reference numerals 15Y,15M, 15C and 15K designate developer conveying rollers configured tofeed developers within the developing units 14Y, 14M, 14C and 14K toportions opposing the photoconductive drums 11Y, 11M, 11C and 11K.Reference numerals 16Y, 16M, 16C, and 16K designate primary transferrollers for respective colors configured to primarily transfer the tonerimages formed on the photoconductive drums 11Y, 11M, 11C and 11K.Reference numeral 17 designates an intermediate transfer belt configuredto carry the primarily transferred toner images. Reference numeral 18designates driving rollers configured to drive the intermediate transferbelt 17. Reference numeral 19 designates a secondary transfer rollerconfigured to transfer the toner images formed on the intermediatetransfer belt 17 to the recording material P, and reference numeral 20designates an opposed secondary transfer roller opposing the secondarytransfer roller 19. Reference numeral 21 designates a fixing unitconfigured to fuse and fix the toner image transferred to the recordingmaterial P while conveying the recording material P. Reference numeral22 designates paper discharging rollers configured to discharge therecording material P after having subjected to the fixing by the fixingunit 21.

Subsequently, an image forming operation of the image forming apparatus1 will be described. Printing data including a printing command andimage information is entered from a host computer or the like, notshown, to the image forming apparatus 1. Then, the image formingapparatus 1 starts the printing operation, and the recording material Pis fed from the paper feed cassette 2 or the paper feed tray 3 by thepaper feed roller 4 a or the paper feed roller 4 b and is fed to aconveying path. The recording material P stops once at the conveyingroller 5 and the opposed conveying roller 6 for synchronization with animage forming operation for forming an image on the intermediatetransfer belt 17 and the timing of conveyance, and waits until the imageformation is performed. Together with an operation to feed the recordingmaterial P, the photoconductive drums 11Y, 11M, 11C and 11K are chargedby the charging rollers 12Y, 12M, 12C and 12K to a certain potential asthe image forming operation. According to the entered printing data, theoptical units 13Y, 13M, 13C and 13K perform scanning and exposure on thesurfaces of the charged photoconductive drums 11Y, 11M, 11C and 11K witha laser beam to form electrostatic latent images thereon. In order tovisualize the formed electrostatic latent images, development isperformed by the developing units 14Y, 14M, 14C and 14K and thedeveloper transfer rollers 15Y, 15M, 15C and 15K. The electrostaticlatent images formed on the surfaces of the photoconductive drums 11Y,11M, 11C and 11K are developed as toner images of respective colors bythe developing units 14Y, 14M, 14C and 14K. The photoconductive drums11Y, 11M, 11C and 11K are in contact with the intermediate transfer belt17, and rotates synchronously with the rotation of the intermediatetransfer belt 17. The developed respective toner images are transferredin sequence on the intermediate transfer belt 17 in an overlapped mannerby the primary transfer rollers 16Y, 16M, 16C and 16K. Then, thesecondary transfer is performed on the recording material P by thesecondary transfer roller 19 and the opposed secondary transfer roller20.

Subsequently, synchronously with the image forming operation, therecording material P is conveyed to the secondary transfer unit in orderto be subject to a secondary transfer. The toner image formed on theintermediate transfer belt 17 is transferred to the recording material Pby the secondary transfer roller 19 and the opposed secondary transferroller 20. The toner image transferred on the recording material P isfixed by the fixing unit 21 composed of fixing rollers or the like. Therecording material P subjected to fixation is discharged onto a paperdischarge tray, not shown, by the paper discharge rollers 22, and theimage forming operation is ended.

In the image forming apparatus 1 shown in FIG. 6, the recording materialdetecting unit 40 is arranged on the upstream side of the conveyingroller 5 and the opposed conveying roller 6 and information reflectingthe surface smoothness of the recording material P conveyed from thepaper feed cassette 2 or the like is detected. Detection of therecording material P by the recording material detecting unit 40 ispreformed after the recording material P is fed from the paper feedcassette 2 or the like into the image forming apparatus before beingclamped between the conveying roller 5 and the opposed conveying roller6. The detection of the recording material P may be performed whilebeing clamped and conveyed between the conveying roller 5 and theopposed conveying roller 6. The reason why the detection of therecording material P is performed while conveying the recording materialP is because the recording material detecting unit 40 employs a linesensor. It is also possible to employ an area sensor, stop theconveyance of the recording material P temporarily, receive reflectedlight from the surface of the recording material P, and pick up an imageof the surface of the recording material P as a matter of course.

(Recording Material Detecting Unit)

FIG. 2 is a perspective view of an interior of the recording materialdetecting unit 40. FIG. 1A is a cross-sectional view of the recordingmaterial detecting unit 40 viewed from a downstream side in thedirection of conveyance of the recording material. FIG. 1B is anenlarged view of a portion indicated by IB in FIG. 1A, that is, of aportion in the vicinity of the reference panel 46 b.

The recording material detecting unit 40 includes light sources(package-type LEDs) 41 a and 41 b configured to irradiate the surface ofa recording material P with light, an imaging lens 42 configured to forman image by the light reflected from the surface of the recordingmaterial P, and a light-receiving unit (line sensor) 43 configured toreceive the light of the image formed by the imaging lens 42 and pick upthe image. The light emitted from the light sources 41 a and 41 b isregulated by slits 44. Reference panels 46 a and 46 b are provided onthe side of the light-receiving unit 43 with respect to the surface ofthe recording material P at ends of an area which is irradiated withlight from the light sources 41 a and 41 b. The reference panels 46 aand 46 b are provided with reference surfaces R as irregular reflectingsurfaces, and light from the light sources 41 a and 41 b is reflectedfrom the reference surfaces R, respectively. The reflected light ispassed through the imaging lens 42 and is received by thelight-receiving unit 43, whereby the amount-of-light adjustment and theshading correction are performed, and the detecting conditions of therecording material detecting unit are controlled. In other words, thereference surfaces R of the reference panels 46 a and 46 b are planeswhich reflect reference reflected light for performing theamount-of-light adjustment and the shading correction to control thedetecting conditions of the recording material detecting unit. Althoughillustration is omitted in FIG. 2, the reference panel 46 b is providedso as to be in line symmetry with the reference panel 46 a with respectto a centerline in FIG. 2 when viewed from the direction of a normalline of the surface of the recording material P.

Provided between the imaging lens 42 and the recording material P is aprotecting member 47 configured to protect the imaging lens 42 frombecoming dirty and allow passage of the reflected light from therecording material P therethrough. These members are supported within aunit body. In particular, the reference panels 46 a and 46 b areplate-shaped members, and are attached on a back surface of a portionguiding the conveyance of the recording material P with a double-facedadhesive material or the like.

Here, the light sources 41 a and 41 b are arranged so that not only thesurface of the recording material P, but also the reference panels 46 aand 46 b are irradiated simultaneously with the light from the lightsources 41 a and 41 b. Therefore, the reflected light reflected from thesurface of the recording material P and the reflected light reflectedfrom the reference surfaces R of the reference panels 46 a and 46 b maybe received simultaneously by the light-receiving unit 43.

The longitudinal directions of the imaging lens 42 and thelight-receiving unit 43 are arranged so as to be orthogonal to thedirection of conveyance of the recording material P. Optical axes of thelight sources 41 a and 41 b are arranged so as to be inclined by anangle of 45° with respect to the direction of conveyance of therecording material P and to intersect each other. The reference panels46 a and 46 b are provided corresponding to the light sources 41 a and41 b respectively, and are provided on both sides of part of the surfaceof the recording material P which reflects the light toward thelight-receiving unit 43 in the direction parallel to the recordingmaterial P and orthogonal to the direction of conveyance of therecording material P. The reference panels 46 a and 46 b are provided onthe side of the light-receiving unit 43 (inner side of the unit) withrespect to the part of the surface of the recording material P whichreflects the light toward the light-receiving unit 43 in the directionof the normal line of the surface of the recording material P. In otherwords, the interior of the recording material detecting unit 40 isconfigured to be line symmetry with respect to a centerline in FIG. 2when viewed from the direction of the normal line of the surface of therecording material P.

FIG. 3 is an operation control block diagram of the recording materialdetecting unit 40. The surface of the recording material P beingconveyed is irradiated with light from the light sources 41 a and 41 b.The reflected light from the recording material P is received by thelight-receiving unit 43 via the imaging lens 42, so that a surface imageis picked up. A surface state of the recording material P such asroughness or the like is reflected on surface image on the recordingmaterial P. The light-receiving unit 43 produces an output of the pickedup surface image on the recording material P to a determining andprocessing unit 45 as a detection device configured to detectinformation on the recording material P and determines the recordingmaterial P. The light-receiving unit 43 is a line sensor having aplurality of pixels aligned in the direction orthogonal to the directionof conveyance of the recording material P. Therefore, the determiningand processing unit 45 converts the surface image of the recordingmaterial P received from the light-receiving unit 43 by an A-D converter451, and obtains one line image orthogonal to the direction ofconveyance of the recording material P. In this example, an 8-bit A-Dconversion IC is used, and the A-D converter 451 produces outputs ofnumerical values from 0 to 255. In an image extractor 452 and a storageunit 455, the surface images of the received recording material P arepieced in the direction of conveyance to obtain a two-dimensionalsurface image.

On the basis of information such as range of effective image or the likestored in the storage area 455, extraction of the surface image to beused for determining the type of the recording material P is performed.At this time, the surface image is subjected to the shading correctionin order to determine the type of the recording material P. Currentvalues for controlling the light emission of the light sources 41 a and41 b, target amount-of-light values required for adjusting the amount oflight, dark current data when the light sources 41 a and 41 b are OFFand data on unevenness of amount of light when the light sources 41 aand 41 b are OFF used for correcting unevenness of amount of light arestored in the storage area 455. In addition, from the data on unevennessof amount of light when the light sources 41 a and 41 b are ON, a pixelrange of data corresponding to the outputs from the reference panels 46a and 46 b (the pixel range which receives the reflected light from thereference panels 46 a and 46 b) and the amount-of-light values thereofare stored. The pixel range of the data on the light sources 41 a and 41b and the amount-of-light values thereof are also stored.

A feature value calculator 453 calculates a feature value of a papertype from the extracted surface image. A paper type determining unit 454determines the paper type on the basis of the result of calculationcalculated by the feature value calculator 453. An output of the resultof determination by the paper type determining unit 454 is supplied toan image forming condition control unit 101 of a control unit (CPU) 10,where the image forming conditions are controlled on the basis of theresult of determination.

The image forming conditions includes conditions such as a transfervoltage, the conveyance speed of the recording material P, andtemperatures of a fixer. For example, if the paper type is determined tobe rough paper as a result of the paper type determination, since fixingproperty is not as good as the image forming conditions for normalpaper, control to make the conveyance speed of the recording material Pslower to increase time used for the fixation by the fixing unit 21 orto increase the fixing temperature is performed.

Referring now to FIGS. 1A and 1B, the arrangement of the referencepanels 46 a and 46 b and the configuration in the periphery of thereference panels 46 a and 46 b, which are characteristics of the presentinvention, will be described. In FIG. 1A, irradiated light irradiatedfrom the light source 41 a to the surface of the recording material P isshown in a double-dashed chain line represented by L1, irradiated lightirradiated toward an end surface, which is not the reference surface R,of the reference panel 46 a is shown in a double-dashed chain linerepresented by L2, and irradiated light irradiated on the referencesurface R of the reference panel 46 a is shown in a double-dashed chainline represented by L3. Since the light to be emitted from the lightsource 41 b is the same as that from the light source 41 a, illustrationis omitted.

End surfaces E of the reference panels 46 a and 46 b and edge portions Cbetween the reference surfaces R and the end surfaces E are covered withlight-shielding portions Sa and Sb provided adjacent to the referencepanels 46 a and 46 b on the inner sides of the recording materialdetecting unit 40 (the center side) with respect to the reference panels46 a and 46 b. Therefore, light is prevented from being reflected fromportions other than the reference surfaces R such as the end surfaces Eof the reference panels 46 a and 46 b or the edge portions C andentering the light-receiving unit 43.

A case where the reference surfaces R are provided on the side of thelight-receiving unit 43 (lower side in the drawing) with respect to thepart of the surface of the recording material P which reflects the lighttoward the light-receiving unit 43 in the direction orthogonal to thesurface of the recording material P will be described. In this case, ifthe reference surfaces R are arranged so as to overlap with the part ofthe surface of the recording material P which reflects the light towardthe light-receiving unit 43, the reflected light from the surface of therecording material P cannot be received by the light-receiving unit 43.Therefore, it is necessary to arrange the reference surfaces R atpositions except for the part of the surface of the recording material Pwhich reflects the light toward the light-receiving unit 43 when viewedfrom the direction orthogonal to the surface of the recording materialP. If the reference surfaces R are arranged under such conditions, thereference surfaces are arranged at a positions where the amount of lightirradiated from the light sources 41 a and 41 b is small rather than thepart of the surface of the recording material P which reflects the lighttoward the light-receiving unit 43. With such an arrangement of thereference panels 46 a and 46 b simply at the positions described above,it is difficult to secure the amount of light of the reflected lightfrom the reference surfaces R received by the light-receiving unit 43.Therefore, in the first embodiment, the reference panels 46 a and 46 bare provided obliquely with respect to the surface of the recordingmaterial P so as to have inclinations α and β toward the light sources,respectively, when viewed from the direction of conveyance of therecording material P. Therefore, in the light directed from the lightsources 41 a and 41 b on to the reference panels 46 a and 46 b, theproportion of the amount of light reflected from the reference surfacesR and entering the light-receiving unit 43 may be increased.

FIG. 4 shows a distribution of brightness (amount-of-light distribution)of the light received by the light-receiving unit 43. A lateral axisrepresents positions on the light-receiving unit 43 corresponding torespective pixels, and a vertical axis represents brightnesscorresponding to the amount of light received by the respective pixels.The pixel position 1 corresponds to a pixel at a right end of thelight-receiving unit 43 in FIG. 1A, and the corresponding pixel on thelight-receiving unit 43 in FIG. 1A goes leftward with an increase in thenumerical value of the pixel position.

Ranges of irradiation on recording material a and b indicate ranges of arecording material surface image to be acquired (pixel ranges thatreceive the reflected light from the surface of the recording materialP) for being used for determining the type of the recording material Pon the basis of the brightness distribution of light irradiated fromlight sources 41 a and 41 b. The ranges of irradiation on the recordingmaterial a and b are set in advance. In these ranges of irradiation onthe recording material a and b, ranges having a brightness exceeding apredetermined threshold value are defined as ranges of effective imageon the recording material, and the surface images within these ranges ofeffective image on the recording material are used for determination ofthe type of the recording material P. In the first embodiment, couplingwith a minimum duration required for the light-receiving unit 43 toreceive the picked up image (to receive light) and the rate of irregularreflection, the threshold value of the brightness is set to 180 in acase where the strength of brightness have 256 tones (0(dark) to255(bright)). In this manner, the reason why the range of effectiveimage of the recording material from the ranges of irradiation on therecording material a and b is for preventing the pixel range used forthe determination of the type of the recording material P from changingdepending on the accuracy of the mounting position of thelight-receiving unit 43.

The ranges of irradiation on the reference panel a and b represent areasfrom which the surface information on the reference surfaces R of thereference panels 46 a and 46 b respectively (the pixel ranges thatreceive the light reflected from the reference panels 46 a and 46 b) areacquired. The ranges of effective image on the reference panel a and bare areas used for calculating the amount of reflected light from thereference surfaces R.

As described above, the reference panels 46 a and 46 b are providedobliquely with respect to the surface of the recording material P so asto have inclinations α and β toward the light sources, respectively,when viewed from the direction of conveyance of the recording materialP. Therefore, peaks having a large amount of light are obtained in theranges of effective image of the reference panel, and hence it isunderstood that a large amount of light is obtained in these pixelranges. When adjusting the amount of emitted light from LEDs as thelight sources 41 a and 41 b, if the amount of reflected light from thereference surfaces R of the reference panels is on the order of ½ theaverage amount of light obtained on the line sensor pixels, a amount oflight sufficient for executing a amount-of-light adjustment with highdegree of accuracy is obtained.

More specifically, the sizes to achieve installation of the referencepanels corresponding to a recording material irradiating window andinstallation at the end portion are such that the length of thereference panel is on the order of 4 to 5 mm and the thickness of resinportion which constitutes the recording material irradiating window ison the order of 2 to 3 mm. Therefore, the allowable height of a spacewhich allows the reference panels to be installed obliquely within arange which does not cause any optical problem is on the order of 0.8 to1.5 mm. To exemplify the further detailed angles of inclination α and β,the angle of inclination is approximately 11° if the length is 5 mm andthe height of inclination is 1 mm and, in the same manner, the angle ofinclination is approximately 20° if the length is 4 mm and the angle ofinclination is 1.5 mm. If the angles of inclination α and β are larger,the reflected light from the reference panels may enter the range ofeffective image of the recording material, which may affect the accuracyof determination.

There are a pixel range having a sagged amount of light between therange of radiation on the reference panel and the range of irradiationon the recording material. It is because the light-shielding portions Saand Sb are members formed of black resin. In other words, by employingblock color for the light-shielding portions Sa and Sb, the amount oflight reflected from the light-shielding portions Sa and Sb and enteringthe light-receiving unit 43 is reduced in comparison with the reflectedlight from the reference surfaces R or the surface of the recordingmaterial P. In other words, the average amount of light per unit pixelof light reflected from the light-shielding portions Sa and Sb andreceived by the light-receiving unit 43 is smaller than the averageamount of light per unit pixel of light reflected from the surface ofrecording material and received by the light-receiving unit 43. Also, inother words, the average amount of light per unit pixel of lightreflected from the light-shielding portions Sa and Sb and received bythe light-receiving unit 43 is smaller than the average amount of lightper unit pixel of light reflected from the reference surfaces R andreceived by the light-receiving unit 43. In other words, thelight-shielding portions Sa and Sb have a low reflecting surface havingan average amount of light per unit pixel of light received by thelight-receiving unit 43 smaller than those of the surface of therecording material P and the reference surfaces R. Since the surfaces ofthe light-shielding portions Sa and Sb are black, the surfaces arelow-reflecting surface in the first embodiment. However, the surfaces ofthe light-shielding portions Sa and Sb may be coated with areflection-resistant coating.

Since the pixel position of the light-receiving unit 43 having a saggedamount of light can be detected clearly, it is possible to detect thepixel positions having the sagged amount of light and determine thewidth of the range of effective image of the recording material simplywith high degree of accuracy with reference to the pixel positionshaving the sagged amount of light.

The light-shielding portions Sa and Sb covers the end surfaces E and theedge portions C of the reference panels 46 a and 46 b. Therefore, thelight from the light sources 41 a and 41 b is prevented from beingreflected from the end surfaces E and the edge portions C, so that thenoise caused by the light reflected from portions other than thereference surfaces R of the reference panels 46 a and 46 b is inhibited.Therefore, a range which could not used as the range of effective imageof the recording material due to the presence of influence of the noisecaused by the light reflected from the portions other than the referencesurfaces R in the related art can now be used as the range of effectiveimage of the recording material. Since the influence of the noise causedby the light reflected from the portions other than the referencesurfaces R is restrained, the position having the sagged amount of lightdescribed above can be detected further clearly.

Although the package-type LEDs are used as the light source in the firstembodiment, chip-type LEDs may also be used. Although the line sensorare used as the light-receiving unit in the first embodiment, an areasensor may be used. The light from the light sources may be caused topass through light guides before being directed to the recordingmaterial P and the reference panels 46 a and 46 b.

In this manner, according to the first embodiment, the reference panels46 a and 46 b are provided obliquely with respect to the surface of therecording material P so as to have inclinations α and β toward the lightsources respectively when viewed from the direction of conveyance of therecording material P. Therefore, a large amount of light is obtained inthe range of effective image of the reference panel, and hence aamount-of-light adjustment with high degree of accuracy can be executedand, consequently, the accuracy of the recoding material determinationmay be improved.

Also, with the provision of the light-shielding portions Sa and Sbhaving low-reflection surfaces, a range having a sagged amount of lightis generated on the pixels of the line sensor 43 between the range ofirradiation on the recording material and the range of irradiation onthe reference panel. The amount of light in this range is smaller incomparison with the amounts of light in these ranges. Then, withreference to the position with the sagged amount of light, the width ofthe range of effective image of the recording material can be determinedsimply with high degree of accuracy and, consequently, the range whichcould not be used as the range of effective image of the recordingmaterial in the related art can now be used as the range of effectiveimage of the recording material. Therefore, improvement of the accuracyof determination of the recording material is achieved.

Also, according to the present invention, by covering the end surfaces Eor the edge portions C with the light-shielding portions Sa and Sb, thenoise caused by the light reflected from the portions other than thereference surfaces R is inhibited, so that the range which could notused as the range of effective image of the recording material due tothe presence of influence of the noise caused by the light reflectedfrom the portions other than the reference surfaces R in the related artcan now be used as the range of effective image of the recordingmaterial. Therefore, if the same light-receiving unit is used, the widerrange of effective image of the recording material than in the relatedart can be obtained, so that the accuracy of determination of therecording material may be improved as a result.

Second Embodiment

Subsequently, a second embodiment of the present invention will bedescribed. The same parts as the first embodiment are designated by thesame reference numerals and the description will be omitted.

FIG. 5 is a cross-sectional view of the recording material detectingunit 40 viewed from a direction parallel to the surface of a recordingmaterial P and orthogonal to the direction of conveyance of therecording material. The second embodiment shows a state in which thereference panels 46 a and 46 b are inclined with respect to the surfaceof the recording material P to provide the reference surfaces R with aninclination gamma γ on the side of the light sources 41 a and 41 b fromthe direction parallel to the surface of the recording material andorthogonal to the direction of conveyance of the recording material P.Even when the reference surfaces R are inclined, the amount of lightwithin the range of irradiation on the reference panel can be increasedand approximately ½ the average amount of light obtained on the sensorpixels can be secured as the amount of reflected light from thereference panels. Therefore, when adjusting the amount of emitted lightfrom the LED as the light sources, a sufficient amount of light isobtained, and hence the amount-of-light adjustment with high degree ofaccuracy can be executed.

It is also possible to provide the reference surfaces R withinclinations α and β toward the light sources 41 a and 41 b when viewedfrom the direction of transport of the recording material P as in thefirst embodiment and, in addition, with an inclination of γ toward thelight sources 41 a and 41 b when viewed in the direction parallel to thesurface of the recording material and orthogonal to the direction oftransport of the recording material P.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

What is claimed is:
 1. A recording material detection apparatuscomprising: a light source configured to irradiate a recording materialwith light; a reference surface to be irradiated with light from thelight source, the reference surface being arranged on the side of thelight source with respect to a recording material in a directionorthogonal to the surface of the recording material; and alight-receiving unit having a plurality of pixels and configured toreceive light reflected from a surface of the recording materialirradiated with the light from the light source and the referencesurface, wherein the reference surface is inclined with respect to apart of the surface of the recording material, which reflects the lighttoward the light-receiving unit, such that the reference surface becomescloser to the light-receiving unit as it becomes farther away from thelight source in an aligned direction of the plurality of pixels.
 2. Therecording material detection apparatus according to claim 1, wherein thereference surface is arranged at a position where the amount of lightirradiated from the light source is smaller than the part of the surfaceof the recording material, which reflects the light toward thelight-receiving unit.
 3. The recording material detection apparatusaccording to claim 1 further comprising: a detecting device configuredto detect information relating to a surface state of the recordingmaterial on the basis of the light reflected from the surface of therecording material and received by the light-receiving unit, thedetecting device controlling conditions for detection of the informationrelating to the surface state of the recording material on the basis ofthe light reflected from the reference surface and received by thelight-receiving unit.
 4. The recording material detection apparatusaccording to claim 1, wherein the reference surface is inclined withrespect to a conveyance direction of the recording material such thatthe reference surface becomes closer to the light-receiving unit as itbecomes farther away from the light source in the conveyance directionof the recording material.
 5. The recording material detection apparatusaccording to claim 1 further comprising: an another reference surface tobe irradiated with light from the light source, the another referencesurface being arranged on the side of the light source with respect tothe recording material in the direction orthogonal to the surface of therecording material, wherein the light-receiving unit receives lightreflected from the another reference surface, wherein the anotherreference surface is inclined with respect to the part of the surface ofthe recording material, which reflects the light toward thelight-receiving unit, such that the another reference surface becomescloser to the light-receiving unit as it becomes farther away from thelight source in the aligned direction of the plurality of pixels, andwherein the part of the surface of the recording material, whichreflects the light toward the light-receiving unit, is arranged betweenthe reference surface and the same one of the other reference surfacesin the aligned direction of plurality of pixels.
 6. A recording materialdetection apparatus comprising: a light source configured to irradiate arecording material with light; a reference surface to be irradiated withlight from the light source, the reference surface being arranged on theside of the light source with respect to a recording material in adirection orthogonal to the surface of the recording material; and alight-receiving unit having a plurality of pixels and configured toreceive light reflected from a surface of the recording materialirradiated with the light from the light source and the referencesurface, wherein the reference surface is inclined with respect to analigned direction of the plurality of pixels such that the referencesurface becomes closer to the light-receiving unit as it becomes fartheraway from the light source in the aligned direction of the plurality ofpixels.
 7. The recording material detection apparatus according to claim5, wherein the reference surface is arranged at a position where theamount of light irradiated from the light source is smaller than a partof the surface of the recording material, which reflects the lighttoward the light-receiving unit.
 8. The recording material detectionapparatus according to claim 6 further comprising: a detecting deviceconfigured to detect information relating to a surface state of therecording material on the basis of the light reflected from the surfaceof the recording material and received by the light-receiving unit, thedetecting device controlling conditions for detection of the informationrelating to the surface state of the recording material on the basis ofthe light reflected from the reference surface and received by thelight-receiving unit.
 9. The recording material detection apparatusaccording to claim 6, wherein the reference surface is inclined withrespect to a conveyance direction of the recording material such thatthe reference surface becomes closer to the light-receiving unit as itbecomes farther away from the light source in the conveyance directionof the recording material.
 10. The recording material detectionapparatus according to claim 6 further comprising: an another referencesurface to be irradiated with light from the light source, the anotherreference surface being arranged on the side of the light source withrespect to the recording material in the direction orthogonal to thesurface of the recording material, wherein the light-receiving unitreceives light reflected from the another reference surface, wherein theanother reference surface is inclined with respect to the aligneddirection of the plurality of pixels such that the another referencesurface becomes closer to the light-receiving unit as it becomes fartheraway from the light source in the aligned direction of the plurality ofpixels, and wherein the part of the surface of the recording material,which reflects the light toward the light-receiving unit, is arrangedbetween the reference surface and the another reference surface in thealigned direction of the plurality of pixels.
 11. An image formingapparatus configured to form an image on a recording materialcomprising: a light source configured to irradiate a recording materialwith light; a reference surface to be irradiated with light from thelight source, the reference surface being arranged on the side of thelight source with respect to a recording material in a directionorthogonal to the surface of the recording material; a light-receivingunit having a plurality of pixels and configured to receive lightreflected from a surface of the recording material irradiated with thelight from the light source and the reference surface; a detectingdevice configured to detect information relating to a surface state ofthe recording material on the basis of the light reflected from thesurface of the recording material and received by the light-receivingunit, the detecting device controlling conditions for detection of theinformation relating to the surface state of the recording material onthe basis of the light reflected from the reference surface and receivedby the light-receiving unit; and a control unit configured to controlconditions for image formation on the recording material on the basis ofan output from the detecting device, wherein the reference surface isinclined with respect to a part of the surface of the recordingmaterial, which reflects the light toward the light-receiving unit, suchthat the reference surface becomes closer to the light-receiving unit asit becomes farther away from the light source in an aligned direction ofthe plurality of pixels.
 12. The image forming apparatus according toclaim 11, wherein the reference surface is arranged at a position wherethe amount of light irradiated from the light source is smaller than thepart of the surface of the recording material, which reflects the lighttoward the light-receiving unit.
 13. The image forming apparatusaccording to claim 11, wherein the reference surface is inclined withrespect to a conveyance direction of the recording material such thatthe reference surface becomes closer to the light-receiving unit as itbecomes farther away from the light source in the conveyance directionof the recording material.
 14. The image forming apparatus according toclaim 11 further comprising: an another reference surface to beirradiated with light from the light source, the another referencesurface being arranged on the side of the light source with respect tothe recording material in the direction orthogonal to the surface of therecording material, wherein the light-receiving unit receives lightreflected from the another reference surface, wherein the anotherreference surface is inclined with respect to the part of the surface ofthe recording material, which reflects the light toward thelight-receiving unit, such that the another reference surface becomescloser to the light-receiving unit as it becomes farther away from thelight source in the aligned direction of the plurality of pixels, andwherein the part of the surface of the recording material, whichreflects the light toward the light-receiving unit, is arranged betweenthe reference surface and the another reference surface in the aligneddirection of the plurality of pixels.
 15. An image forming apparatusconfigured to form an image on a recording material comprising: a lightsource configured to irradiate a recording material with light; areference surface to be irradiated with light from the light source, thereference surface being arranged on the side of the light source withrespect to a recording material in a direction orthogonal to the surfaceof the recording material; a light-receiving unit having a plurality ofpixels and configured to receive light reflected from a surface of therecording material irradiated with the light from the light source andthe reference surface; a detecting device configured to detectinformation relating to a surface state of the recording material on thebasis of the light reflected from the surface of the recording materialand received by the light-receiving unit, the detecting devicecontrolling conditions for detection of the information relating to thesurface state of the recording material on the basis of the lightreflected from the reference surface and received by the light-receivingunit; and a control unit configured to control conditions for imageformation on the recording material on the basis of an output from thedetecting device, wherein the reference surface is inclined with respectto an aligned direction of the plurality of pixels such that thereference surface becomes closer to the light-receiving unit as itbecomes farther away from the light source in the aligned direction ofthe plurality of pixels.
 16. The image forming apparatus according toclaim 15, wherein the reference surface is arranged at a position wherethe amount of light irradiated from the light source is smaller than apart of the surface of the recording material, which reflects the lighttoward the light-receiving unit.
 17. The image forming apparatusaccording to claim 15, wherein the reference surface is inclined withrespect to a conveyance direction of the recording material such thatthe reference surface becomes closer to the light-receiving unit as itbecomes farther away from the light source in the conveyance directionof the recording material.
 18. The image forming apparatus according toclaim 15 further comprising: an another reference surface to beirradiated with light from the light source, the another referencesurface being arranged on the side of the light source with respect tothe recording material in the direction orthogonal to the surface of therecording material, wherein the light-receiving unit receives lightreflected from the another reference surface, wherein the anotherreference surface is inclined with respect to the aligned direction ofthe plurality of pixels such that the same one of the other referencesurfaces becomes closer to the light-receiving unit as it becomesfarther away from the light source in the aligned direction of theplurality of pixels, and wherein the part of the surface of therecording material, which reflects the light toward the light-receivingunit, is arranged between the reference surface and the anotherreference surface in the aligned direction of the plurality of pixels.